A guard stands at the entrance to the California state prison at San Quentin. Photograph: Justin Sullivan/Getty Images

In 1981, when Randall Ellis was 16 years old, he participated in a robbery in which his co-defendant shot and killed a young store clerk. Because he took part in a robbery that led to a murder, he was found guilty of the murder and was tried as an adult by the state of California, which chose to impose the maximum sentence the law would allow, of 25 years to life.

Thirty-one years later, Randall is still in prison and his chances of ever being released are slim at best.

There are around 32,000 inmates, 20% of California's total prison population, in the "lifer" category to which Randall now belongs. Approximately 8,000 of them are "three strikes" offenders. Being a lifer means you received a sentence of "15 to life" or "25 to life", so you must serve out the 15 years or the 25 years (or whatever number you were assigned) before you become eligible for parole. These lifers, known as LWPs (life with parole) do not include the much smaller category of prisoners known as LWOP (life without parole) who committed crimes so heinous they were sentenced effectively to die in prison. But it appears that the line between LWPs and LWOPs has become increasingly blurred, as so few prisoners are being granted parole in the past 20 years that "to life" is starting to seem an awful lot like "for life".

This means, of course, that the number of older and geriatric prisoners are growing. By the end of 2009, there were 11,000 prisoners over the age of 55. (Prisoners' physiological age tends to be 10-15 years more their chronological age due to the stress of incarceration, so 55 counts as elderly.) This number is expected to triple to over 30,000 within the next decade or so (pdf), which will put extraordinary pressure on a state that is already being bankrupted in part by its overcrowded prisons.

Randall turned 47 this month, and although he believes he should have been let out at least ten years ago, statistically, his chances of growing old in prison are far greater than his chance of being released.

"I've been kept here way past any reasonable period of time, considering that I was just a kid in the wrong place, with the wrong people to begin with. Over the years, the justifications have changed. They don't even consider my age, and somehow put me beyond the thinking capacity of a 16 year-old who made bad choices to somehow being beyond that."

I don't know if Randall should have been released ten years ago or not. The parole board obviously has better knowledge of whether or not he may still be a threat to society. He does raise an interesting point, however, that a person's motivations and understanding are very different at 47 than they were at 16. Statistics consistently show that people tend to "age out of crime" (pdf). Nationwide, the recidivism rate for inmates aged between 16 and 29 is over 50%; for inmates 55 and older, the rate drops to 2%, rendering the chance of an elderly inmate re-offending upon release almost negligible.

But still, they remain locked up. In 2008, for instance, 7,308 lifers were eligible for parole. Only 294 were approved by the parole board, and of those, 81 were denied by then Governor Arnold Schwarzenegger, and more than 30 were sent back for review. In the end, fewer than 60 inmates were released. There has been a slight improvement in the number of paroles granted since Governor Brown took over, but still, more than 80% of requests are denied.

Public safety is generally cited as the reason for keeping people in prison indefinitely, and no one – least of all a politician who will be facing re-election – wants their signature on the parole form of an inmate who murders somebody's loved one upon their release. Considered in that light, granting parole is not a decision to be taken lightly.

But the fact remains that the billions of dollars spent each year keeping prisoners locked up for life are billions being diverted from the kinds of programs that might have prevented them from getting locked up in the first place.